Bi-metallic switch element

Abstract: A bi-metallic switch element 10 has a contact wire 26 attached thereto by means of a plurality of crimps. A first crimp 28 applied at a first pressure fixes the contact wire to the element and a second crimp 30, formed at a lesser, more controlled pressure aligns the contact wire in a predetermined location.

Description: TECHNICAL FIELD This invention relates generally to bi-metallic switch elements and more particularly to such elements having better control over the location of a contact wire which is a part of the element. The element can form a part of a switch which can be employed in the starting circuitry of high intensity discharge lamps. BACKGROUND ART The basic elements of a bi-metal switch include at least a bi-metal member which usually is elongated and which can have a contact wire attached thereto. Generally, it is important that the contact wire be accurately positioned on the bi-metal. Two major forms of attachment have been employed in the past. A first simply involves welding the contact wire to the bi-metal and a second involves attaching the wire by means of a crimp. The latter method has been accomplished by stamping either a tunnel or a pair of tabs from the bi-metal, laying a wire in the opening thus provided, and crimping the tabs or tunnel to the wire. While these methods provided an adequate holding means for the wire they did not provide for accurate location, since very often the force applied to fix the wire disturbed whatever previous location had been determined. US-A-5,187,416 according to the precharacterizing part of claim 1 discloses bi-metallic switch element which comprises an elongated bi-metallic member consisting of a relatively high expansion material and a relatively low expansion material in an operative, intimate contact with one another. One tunnel is provided in a first end of said bi-metallic member which projects upwardly for inserting and fixing an electrically conductive conduct wire to said tunnel. DISCLOSURE OF THE INVENTION It is, therefore, an object of the invention to obviate the disadvantages of the prior art. It is another object of the invention to enhance bi-metal switch elements. Yet another object of the invention is the enhancement of the operation of bi-metal switch elements. These objects are accomplished, in one aspect of the invention, by the provision of a bi-metallic switch element which comprises an elongated bi-metallic member having a longitudinal axis and comprised of a relatively high expansion material and a relatively low expansion material in operative, intimate contact with one another. Two spaced apart tunnels are formed in a first end of the member and project upwardly from the high expansion material. The tunnels are formed transverse to the longitudinal axis. An elongated, electrically conductive contact wire has one end thereof positioned in the tunnels. Crimps are formed in the tunnels with a first crimp being formed in a first of the tunnels fixing the wire to the bi-metallic element and a second crimp being forned in a second of the tunnels for positioning the wire in a predetermined location relative to the bi-metallic element. The employment of the plural tunnels allows for the use of differential pressures for each of the crimps and provides for control over the location of the contact wire. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a bi-metallic element having a pair of contact wire receiving tunnels formed in one end thereof; Fig. 2 is a perspective view of a bi-metallic element with a contact wire crimped in the tunnels; and Fig. 3 is a side elevational view of a bi-metallic element illustrating a placement of the contact wire. BEST MODE FOR CARRYING OUT THE INVENTION For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings. Referring now to the drawings with greater particularity, there is shown in Figs. 2 and 3 a bi-metallic switch element 10 which comprises an elongated bi-metallic member 12, shown by itself in Fig. 1, having a longitudinal axis 14 and comprised of a relatively high expansion material 16 and a relatively low expansion material 18 in operative, intimate contact with one another. A suitable material is ASTM B388 Type TM5. Two spaced apart tunnels 20 and 22, respectively, are formed in a first end 24 of member 12 and project upwardly from the high expansion material 16. An opposite end of the element 12 has a right angle bend formed therein to provide a wall 23. The tunnels are formed transversely to the longitudinal axis. An elongated, electrically conductive contact wire 26, which preferably is formed from a high tensile tungsten wire such as NS-55N which is avaliable from OSRAM SLYVANIA, Townada, Pennsylvania 18848, has one end thereof positioned in the tunnels. (As used herein, high tensile designates wire having a strength of 67-72 gm/mg/200m). A first crimp 28 is formed in a first of the tunnels, e.g., 20, to fix the wire 26 to the bi-metallic element 12. The crimp 28 causes an asymmetric rupture of the tunnel, as is shown in Fig.2, and provides what appears to be a pair of tabs 28a and 28b. The asymmetry is caused by the use of an offset clamping punch. A first, relatively high pressure is employed to form the crimp 28. A second crimp 30 is formed in the second tunnel 22 and is used to position the wire in a predetermined position relative to the bi-metallic element 12. The second crimp 30 also provides an asymmetric rupture of the tunnel to form tabs 30a and 30b. These latter tabs are asymmetric with respect to the tabs 28a and 28b and both sets of tabs are asymmetric with respect to the centerline 14. The second crimp 30 is preferably formed at a lower pressure than the first crimp to aid in positioning the location of the wire. This can be accomplished by making the second set of clamping tools slightly longer than the first set. In the embodiment of the invention shown and described below, the second set of tools can be 0.003" (0.0076mm) longer than the first set. The preferred location of the contact wire 26 is contiguous with the surface of the element 12 and aligned along centerline 14. As shown in Fig.3 by the dimension "A", a small tolerance is acceptable. In a preferred form of the invention the tolerance should be no greater than 1mm for a switch element having a length of 0.875" (2.223mm) and a width of 0.125" (0.318mm). The tunnels have a width of about 0.040" (0.102mm) and can be separated by about 0.046" -0.050" (0.117-0.127mm). The transverse length of the tunnels is about 0.0625" (0.158mm). While not limited thereto, the switch 10 described herein has greatly improved the operation of high intensity discharge lamps by providing an accurate cycle time over the life of the lamps. While there have been shown and described what are at present considered to be the preferred embodiments of the invention, it will be apparent to those skilled in the art that various changes and modifications can be made herein without departing from the scope of the invention as defined by the appended claims.

Claims: A bi-metallic switch element comprising: an elongated bi-metallic member (12) having a longitudinal axis (14) and comprised of a relatively high expansion material (16) and a relatively low expansion material (18) in operative, intimate contact with one another, wherein at least one tunnel (20;22) is formed in a first end (24) of said member (12) and projected upwardly from said high expansion material (16), arcuate projections forming said at least one tunnel (20;22) being transverse to said longitudinal axis (14), characterized in that two spaced apart tunnels (20,22) are formed in the first end (24) of said member (12) and project upwardly from said high expansion material (16), arcuate projections forming both tunnels (20,22) being transverse to said longitudinal axis (14). The bi-metallic switch element of claim 1 wherein an elongated, electrically conductive contact wire (26) has one end thereof positioned in said tunnels (20,22). The bi-metallic switch element of claim 2 wherein another end of said contact wire (26) projects beyond a second end (23) of said elongated bi-metallic element (12). The bi-metallic switch element of claim 3 wherein each of said tunnels (20,22) is crimped to said wire (26), each of said tunnels (20,22) thereby separated into two tabs (28A,28B;30A,30B) said tabs (28A,28B;30A,30B) being asymmetric with respect to a centerline of said elongated bi-metallic member (12), and the tabs (28A,28B) of the (20) first of said tunnels (20,22) being asymmetric with respect to the tabs (30A,30B) of the second (22) of said tunnels (20,22) . The bi-metallic switch element of claim 1 wherein crimps (28,30) are formed in said tunnels (20,22), wherein a first crimp (28) formed in a first (20) of said tunnels (20,22) fixing an elongated, electrically conductive contact wire (28) to said bi-metallic element (12) and a second crimp (130) formed in a second (22) of said tunnels (20,22) positioning said wire (26) in a predetermined location relative to the bi-metallic element (12).

Inventors: BAZIN SIMONE P, KULIK JOSEPH S, VINCENT ROBERT J, BAZIN, SIMONE P., KULIK, JOSEPH S., VINCENT, ROBERT J.
Applicants: GTE PROD CORP, OSRAM SYLVANIA INC.
Application year: 1994
Main classification: H01H37
IPC codes: H01H1, H05B41, H01H37